Signal substitution system

ABSTRACT

A first selector is to be set up to cause the control tone produced by a variable frequency oscillator to have a first selected frequency. A second selector is set up to cause the control tone to have a second selected frequency. A third selector set at a third selected frequency determines which of the first or second selectors is operable to control the oscillator. The second selector is operative to cause the control tone to have the second selected frequency when the first and third selectors are set in corresponding conditions, and the first selector is operative to cause the control tone to have the first selected frequency when the first and third selectors are set in noncorresponding conditions.

wilted States Patent [191 Wycott [4 1 Sept. 3, 1974 SIGNAL SUBSTITUTIONSYSTEM [76] Inventor: Keith H. Wycoff, PO. Box 308,

Lexington, Nebr. 68850 [22] Filed: Apr. 12, 1972 [21] Appl. No.: 243,150

Related US. Application Data [63] Continuation of Ser. No. 75,417, Sept.25, 1970,

abandoned.

[56] References Cited UNITED STATES PATENTS 10/1961 Faulkner 331/179 Xl/l968 Driver 325/64 X 7/1968 B0558 et a1 331/177 V X 2/1969 Abramson331/117 R Primary ExaminerHerman Karl Saalbach AssistantExaminerSiegfried H. Grimm [5 7 ABSTRACT A first selector is to be setup to cause the control tone produced by a variable frequency oscillatorto have a first selected frequency. A second selector is set up to causethe control tone to have a second selected frequency. A third selectorset at a third selected frequency determines which of the first orsecond selectors is operable to control the oscillator. The secondselector is operative to cause the control tone to have the secondselected frequency when the first and third selectors are set incorresponding conditions, and the first selector is operative to causethe control tone to have the first selected frequency when the first andthird selectors are set in noncorresponding conditions.

38 Claims, 5 Drawing Figures mammw awn 3328.861

SHEEI 2 (IF 5 as 66- GATED AMP33 609 ea 64 265 6g 2 GATED AMP PAIENIED31w 3.833.861

2 32? FIG. 3 26| 2 M 267 SWITCH I 2769 SELECTOR SWITCH SWITCH a, 362.5ELECTRONIC 36l SIGNAL SUBSTITUTION SYSTEM This is a continuation of thecopending application of Keith H. Wycoff, US. Pat. Ser. No. 75,417,filed Sept. 25, 1970, for TONE SUBSTITUTION SYSTEM now abandoned.

It is an important object of the present invention to provide animproved tone substitution system for use in a transmitter of the typecapable of sending a tone or set of tones to alert a remote receiver,which tone substitution system automatically substitutes a differenttone or set of tones for the tone or tones selected.

Another object of the invention is to provide an improved tonesubstitution system which incorporates only electronic and manualswitching, and does not incorporate patch-cords or the like.

Yet another object of the invention is to provide a tone substitutionsystem capable of substituting any available tone or set of tones forthe tone or tones actually selected.

Still another object of the invention is to provide an improved tonesubstitution system which is capable of substituting up to all of theavailable tones or sets of tones for the tone or sets of tones selected.

A further object of the invention is to provide a paging system in whicha faulty receiver that is adapted to respond to a given tone or set oftones may be permanently replaced with a receiver adapted to respond toa different tone or set of tones.

In connection with the foregoing object, it is a further object toprovide a tone substitution system which enables the faulty receiver tobe repaired and then be used as a spare to replace another faultyreceiver.

A still further object of the invention is to provide a tonesubstitution system which enables individuals to transfer their callsfrom their own selective calling receivers to the selective callingreceiver of another, yet permitting the other to continue to receivecalls directed to him.

Another object of the invention is to provide an improved tonesubstitution system which requires no particular tones or sets of tonesto be set aside for use in connection with receivers used as spares.

In summary, there is provided a tone substitution system for use in atransmitter and comprising tone signal producing means, first selectormeans coupled to the tone signal producing means and placeable in one ofa plurality of conditions to cause the tone signal to have a selectedone of a corresponding plurality of first characteristics, secondselector means coupled to the tone signal producing means and placeablein one of a plurality of conditions to cause the tone signal to have aselected one of a corresponding plurality of second characteristics, andthird selector means coupled to the first and second selector means andplaceable in one of a plurality of conditions for rendering the firstselector means or the second selector means operative to control thecharacteristics of the tone signal, the tone signal having the selectedone of the first characteristics when the conditions of the first andthird selector means do not correspond, the tone signal having theselected one of the second characteristics when the conditions of thefirst and third selector means correspond.

Further features of the invention pertain to the particular arrangementof the elements of the transmitter and the tone substitution systemtherein, whereby the above outlined and additional operating featuresthereof are attained.

The invention, both as to its organization and the method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawings, in which:

FIG. 1 is a block diagram of a transmitter incorporating therein a tonegenerator which includes the tone substitution system incorporating thenovel features of the present invention;

FIG. 2 is a schematic diagram of the tone substitution system;

FIG. 3 illustrates an alternative form of a portion of the tonesubstitution system; and

FIGS. 4 and 5 illustrate a block diagram illustrating further featuresof the invention.

Referring now to FIG. 1 of the drawings, there is shown a communicationtransmitter 20 which is adapted to generate an RF carrier wave modulatedselectively by audio signals and one or more control tones. Basically,the transmitter 20 is for use in a selective calling communicationsystem which comprises, in addition to the transmitter, a number ofreceivers, all capable of processing the same frequency carrier wave.Each receiver is squelched in its stand-by condition and isautomatically unsquelched with the carrier wave modulated by the propercontrol tone or set of control tones for which that receiver isdesigned. Each receiver will respond to a differentcontrol tone or setof control tones, whereby the operator of the transmitter can call aselected receiver without energizing any of the other receivers. In acommunication system equipped to transmit and receive voice, theoperator at the transmitter, wishing to communicate with a specificreceiver or receivers, selects the proper set of control tones for thatreceiver, which tones are modulated on the carrier wave. The selectedreceiver will become unsquelched, whereupon the operator can actuate thepush-to-talk switch and speak into the microphone. Sounds, of course,are converted into audio signals which are modulated on the carrierwave, the modulated carrier wave being processed by the selectedreceiver and reconverted to sound waves.

In such selective calling communication systems, a receiver may becomefaulty and in need of repair. In such case, it is desirable that theindividual be given a different receiver while the faulty one is beingrepaired. It is unlikely that a receiver would be available that wouldbe responsive to the same tone or tones to which the individualsoriginal receiver was programed. Instead, the individual will be given areceiver responsive to a different tone or tones. It would beimpractical to advise all pertinent persons who may have occasion tocall the individual that his number has been changed. On the other hand,the instant invention enables the transmitter to be simply and rapidlyadjusted so that the operator can select the individuals originalnumber,

but the transmitter transmits the tone or set of tones which activateshis new receiver. Such a system functions in a similar fashion if usedin connection with the telephone system. In other words, a persondesiring to get in touch with the individual would dial the originalnumber of the individual. The transmitter would, however, transmit thetone or tones to activate his new receiver.

Referring back to FIG. 1, the transmitter includes an RF oscillator 21which develops on its output a relatively low frequency oscillatorysignal. An audio amplifier 22 has its output coupled to a first input ofa modulator 23, the second input thereof being coupled to the oscillator21. The signals from the audio amplifier 22, which may be either audiosignals produced by conversion of sound waves applied to the microphone24 or the control tones, are modulated by the modulator 23 onto therelatively low frequency oscillatory signal. The modulator oscillatorysignals are applied to a frequency multiplier 25 which increases thefrequency of the oscillatory signal. The relatively high frequencysignal is applied to a power amplifier 26 where the signal strength isincreased, thereby to provide a high level, frequency-multiplied carrierwave which is emitted from an antenna 27.

Associated with the microphone 24 is a push-to-talk switch 30 whichcouples a B+ DC voltage to a first pulse generator 31, the output ofwhich is coupled to a second pulse generator 32. The output of the firstpulse generator 31 is also coupled to a first gated amplifier 33, andthe output of the second pulse generator 32 is coupled to a second gatedamplifier 34. The outputs of the gated amplifiers 33 and 34 arerespectively coupled through and amplified by the signal amplifiers 35and 36 and then combined across a load resistor 37. The junction of thetwo amplifiers 35 and 36 is coupled to one of the inputs of the audioamplifier 22.

In operation, actuation of the push-to-talk switch 30 in preparation tospeaking into the microphone 24, causes the B+ voltage to be coupled tothe first pulse generator 31 which causes a pulse 38 of predeterminedduration to be produced at the output thereof. The pulse 38 is coupledto the second pulse generator 32 and causes the same to produce a pulse39 commencing at the termination of the pulse 38 and lasting for asecond predetermined duration. The pulses 38 and 39 are coupled to theirrespective gated amplifiers to render the same operative for therespective durations of the pulses. The tone generator 40, the detailsof which will be presently described, has one output thereof coupled toa second input of the gated amplifier 33 and has another output thereofcoupled to the second input of the gated amplifier 34. When the gatedamplifier 33 becomes activated by virtue of the pulse 38 being appliedthereto, the amplifier amplifies the tone applied thereto from the tonegenerator 40, which tone is then applied to the amplifier 35 and isamplified therein to appear across the load resistor 37. The pulse 39,which commences upon termination of the pulse 38, activates the gatedamplifier 34 so that it can amplify the tone applied thereto from thetone generator 40. The amplified tone is applied to the amplifier 36wherein it is amplified and is applied across the load resistor 37 Itmay be seen, therefore, that across the load resistor 37 appears asequence of two control tones, the first control tone persisting for aduration equal to the duration of the pulse 38 and the second controltone persisting for a duration equal to the duration of the pulse 39.This sequence of control tones is applied to the audio amplifier 22wherein it is amplified, then modulated on the carrier wave aspreviously described. The oscillatory signal modulated by the controltones is increased in frequency by the frequency multiplier 25 andincreased in amplitude by the power output amplifier 26 and radiated bythe antenna 27. The receiver which is tuned to this particular sequenceof control tones will become unsquelched and, therefore, operative toreceive audio signals applied thereto. The operator then may speak intothe microphone 24 which converts the sound waves into electrical signalsthat are modulated onto the carrier wave and transmitted to the selectedreceiver which then demodulates the same and reconverts them into soundwaves, Further details of the construction of the elements 30-39 are notbelieved to be necessary to the description of the invention herein.However, should further information be needed on the manner in whichthese elements are constructed and interconnected, reference may be madeto the inventors copending U.S. Pat. application, Ser. No. 16,037, filedMar. 3, 1970, now U.S. Pat. No. 3,619,784.

Referring now to FIG. 2, the details of construction of the tonegenerator 40 will be described. There is provided a rotary selectorswitch 50 having a movable contact 51 and ten stationary contacts52.1-52.10. The fixed contact 52.2 is coupled to an electronic switch60.2, the electronic switch 60.2 including a resistor 61 coupled betweenthe contact 52.2 and the base of an NPN transistor 62, the collector ofwhich is coupled to the B+ supply voltage. A resistor 63 is coupledbetween the base of the transistor 62 and ground reference potential. Adiode 64 and a resistor 65 are coupled in series between the emitter ofthe transistor 62 and the base of a second NPN transistor 66, theemitter of which is grounded and the collector of which is coupled to avariable frequency oscillator 70.

The oscillator includes a PNP transistor 71 having its emitter coupledthrough a resistor 72 to the B+ supply voltage, the base of thetransistor 71 being coupled through a resistor 77 to ground referencepotential and a resistor 73 coupled back to the B+ voltage. A pair ofserially connected capacitors 74 and 75 is coupled between the collectorof the transistor 71 and ground reference potential, the juncture of thecapacitors 74 and 75 being coupled to the emitter of the transistor 71.An inductor 76 is coupled also to the collector of the transistor 71 andis effectively in parallel with the capacitors 74 and 75 as will bepresently described. The inductor 76 has ten taps 76.1-76.10, onlycertain of the taps having been labeled for convenience. The tap 76.2 ofthe inductor 76 is coupled back to the collector of the transistor 66 inthe electronic switch 60.2.

In operation, the movable arm 51 of the rotary selector switch 50 may bemoved to engage the fixed contact 52.2, whereupon a path is completedfrom the B+ sup ply voltage through the resistor 61 to cause conductionof the transistor 62 through the diode 64, the resistor 65 and thebase-emitter junction of the transistor 66. The transistor 66 thusbecomes saturated and effectively grounds the collector thereof, whichin turn effectively grounds the tap 76.2 on the inductor 76.Accordingly, that portion of the inductor 76 above the tap 76.2 will bein parallel with the serially connected capacitors 74 and 75, whichparallel combination will determine the frequency of a control tonedeveloped by the oscillator 70 at the juncture of the capacitors 74 and75.

The fixed contact 52.9 of the rotary selector switch 50 is coupled toanother electronic switch 60.9, which electronic switch includes thesame parts and is of the same construction as the electronic switch60.2. The parts of the electronic switch 60.9 are labeled with the samereference numerals used to label the corresponding parts in theelectronic switch 60.2. If the movable arm 51 of the rotary selectorswitch 50 is moved to engage the fixed contact 52.9, a path will bedefined for current to flow from the B+ supply voltage to cause thetransistors 62 and 66 in the electronic switch 60.9 to conduct aspreviously described with reference to the electronic switch 60.2.Conduction of the transistor 66 effectively grounds the collectorthereof, thereby grounding the tap 76.9 on the inductor 76 in theoscillator 70. This places the quantity of inductor above the tap 76.9in parallel with the capacitors 74 and 75 to cause the oscillator 70 tooscillate at a frequency lower than the frequency at which theoscillator 70 oscillated with the contact 51 in position to engage thecontact 52.2.

It is to be understood that, although only two electronic switches 60.2and 60.9 have been shown, there will be such electronic switches60.1-60.10 respectively coupling the contacts 52.1-52.10 to the taps76.1-76.10 in the oscillator 70. By moving the arm 51 to the desiredfixed contact, the associated electronic switch will be renderedoperative to couple a predetermined portion of the inductor 76, incircuit with the rest of the oscillator 70, thereby to select thefrequency of the control tone produced by the variable frequencyoscillator 70. Each position of the movable arm 51, therefore,corresponds to a different control tone.

Corresponding circuitry is provided to generate the second control tonein the sequence of control tones, which circuitry is labeled withnumerals corresponding to those used in connection with the circuitryprovided in the first control tone, except that 30 has been added toeach number. Specifically, there is provided a rotary switch 80 having amovable contact 81 and 10 stationany contacts 82.1-82.10. The fixedcontact 82.4 is coupled to an electronic switch 90.4, the electronicswitch 90.4 including a resistor 91 coupled between the contact 82.4 andthe base of an NPN transistor 92, the collector of which is coupled tothe 13+ supply voltage. A resistor 93 is coupled between the base of thetransistor 92 and ground reference potential. A diode 94 and a resistor95 are coupled in series between the emitter of the transistor 92 andthe base of a second NPN transistor 96, the emitter of which is groundedand the collector of which is coupled to a variable frequency oscillator100.

The oscillator 100 includes a PNP transistor 101 having its emittercoupled through a resistor 102 to the B+ supply voltage, the base of thetransistor 101 being coupled through a resistor 107 to ground referencepotential and a resistor 103 coupled back to the B+'voltage. A pair ofserially connected capacitors 104 and 105 is coupled between thecollector of the transistor 101 and ground reference potential, thejuncture of the capacitors 104 and 105 being coupled to the emitter ofthe transistor 101. An inductor 106 is coupled also to the collector ofthe transistor 101 and is effectively in parallel with the capacitors104 and 105 as will be presently described. The inductor 106 has 10 taps1061-10610, only certain of the taps having been labeled forconvenience. The tap 106.4 of the inductor 106 is coupled back to thecollector of the transistor 96 in the electronic switch 90.4.

In operation, the movable arm 81 of the rotary selector switch 80 may bemoved to engage the fixed contact 82.4, whereupon a path is completedfrom the B+ supply voltage through the resistor 91 to cause conductionof the transistor 92 through the diode 94, the resistor and thebase-emitter junction of the transistor 96. The transistor 96 thusbecomes saturated and effectively grounds the collector thereof, whichin turn effectively grounds the tap 106.4 on the inductor 106.Accordingly, that portion of the inductor 106 above the tap 106.4 willbe in parallel with the serially connected capacitors 104 and 105, whichparallel combination will determine the frequency of a control tonedeveloped by the oscillator at the juncture of the capacitors 104 and105.

The fixed contact 82.7 of the rotary selector switch 80 is coupled toanother electronic switch 90.7, which electronic switch includes thesame parts and is of the same construction as the electronic switch90.4. The parts of the electronic switch 90.7 are labeled with the samereference numerals used to label the corresponding parts in theelectronic switch 90.4. If the movable arm 81 of the rotary selectorswitch 80 is moved to engage the fixed contact 82.7, a path will bedefined for current to flow from the B+ supply voltage to cause thetransistors 92 and 96 in the electronic switch 90.7 to conduct aspreviously described with reference to the electronic switch 90.4.Conduction of the transistor 96 effectively grounds the collectorthereof, thereby grounding the tap 106.7 on the inductor 106 in theoscillator 100. This places the quantity of inductor above the tap 106.7in parallel with the capacitors 104 and to cause the oscillator 100 tooscillate at a frequency lower than the frequency at which theoscillator 100 oscillated with the contact 81 in position to engage thecontact 82.4. a

It is to be understood that, although only two electronic switches 90.4and 90.7 have been shown, there will be ten such electronic switches90.1-90.10 respectively coupling the contacts 82.1-82.10 to the taps1061-10610 in the oscillator 100. By moving the arm 81 to the desiredfixed contact, the associated electronic switch will be renderedoperative to couple a predetermined portion of the inductor 106 incircuit with the rest of the oscillator 100, thereby to select thefrequency of the control tone produced by the variable frequencyoscillator 100. Each position of the movable arm 81, therefore,corresponds to a difference control tone.

The details of the tone substitution system will now be described. Thereis provided a rotary selector switch 110 having a movable contact 111and ten stationary contacts 112.10.10. The contact 112.2 is coupled tothe junction of the resistors 61 and 63 in the electronic switch 60.2,and the contact 112.9 is coupled to the junction of the resistors 61 and63 in the electronic switch 60.9. Although not shown, it is to beunderstood that the rest of the stationary contacts l12.10.10 arecoupled respectively to the junction of the resistors 61 and 63respectively in the electronic switches 60.10.10. The movable contact111 of the rotary selector switch 110 is coupled to a first AND circuit120. The AND circuit includes a first NPN transistor 121 having itsemitter coupled to the collector of a second NPN transistor 122, theemitter of which is coupled to ground reference potential. The collectorand base of the transistor 121 are connected together and to the movablecontact 111 of the selector switch 110. Alternatively, a simple diodecould be used in place of the transistor 121. The base of the transistor121 provides a first input to the AND circuit 120 and is coupled to themovable contact 11 1. There is provided another rotary selector switch130 having a movable contact 131 and stationary contacts 132.10.10.

The movable contact 131 is coupled to a second AND circuit 140 whichincludes a first NPN transistor 141 having its emitter coupled to thecollector of a second NPN transistor 142, the emitter of which isgrounded. The base of the transistor 142 is coupled through a resistor143 back to the movable contact 111 of the selector switch 110, andprovides a first input to the AND circuit 140. The base of thetransistor 141 is connected to the movable contact 131 of the rotaryswitch 130 and therefore provides a second input to the AND circuit 140.A second input to the AND circuit 120 is provided by the connectionprovided by the conductor 145 from the contact 131 to the base of thetransistor 122. The collector of the transistor 141 is coupled to anelectronic switch 150 which includes a PNP transistor 151, the base ofwhich is coupled through a resistor 152 to the collector of thetransistor 141 in the AND circuit 140. The emitter of the transistor 151is coupled to the B+ supply voltage and is also coupled through aresistor 153 back to the collector of the transistor 141. The collectorof the transistor 151 is coupled to the junction of a pair of resistors154 and 155.

The resistor 154 in turn coupled to the movable contact 161 of ,a rotaryselector switch 160, which rotary selector switch 160 includes ten fixedcontacts 162.1-0.10, that are connected to the junction of the diode 64and the resistor 65 respectively in the ten electronic switches60.1-0.10. The resistor 155 is coupled to the movable contact 171 ofanother rotary selector switch 170, which also includes 10 fixedcontacts l72.l0.10 that are connected to the junction of the diode 94and the resistor 95 respectively in the ten electronic switches90.10.10.

In the following description of the manner in which the tonesubstitution system operates, a sequence of tones identified by thenumber 97 means that the first tone is represented by position 9 and thesecond tone is represented by position 7. It is to be understood that asequence of tones such as 97 means that the first tone is produced bythe first oscillator 70 when the portion of the inductor above the tap76.9 is in circuit, and that the second tone is produced by the secondoscillator 100 when the portion of the inductor above the tap 106.7 isin circuit. If the operator wants to send sequence 48, he will adjustthe selector switch 1 10 such that the movable contact 51 engages thefixed contact 52.4 (representing the first tone 4) and will set themovable contact 81 of the selector switch 80 to engage the fixed contact82.8 (the second tone 8). Suppose, however, that the receiver to respondto sequence 97 was faulty and has been'replaced with a receiver thatwill respond to sequence 24. The tone substitution system is programedsuch that, if the caller selects sequence 97, sequence 24 will be sentinstead. To effect this programing, the transmitter operator adjusts themovable contact 111 of the selector switch 110 to engage the fixedcontact 112.9 to match the first tone to be substituted (9); and adjuststhe movable contact 131 of the selector switch 130 to engage the contact132.7, which represents the second tone to be substituted (7). Theselector switches 110 and 130 are thus adjusted to represent thesequence of tones that is to be replaced, that is, 97. The selectorswitch 160 is adjusted such that the movable arm 161 engages the contact162.2 and the movable arm 171 of the selector switch 170 is moved toengage the fixed contact 172.4. Thus, the selector switches 160 and 170are adjusted to represent the sequence of tones to be substituted, thatis, sequence 24. Now the tone substitution system is properly programed.

If the operator sets the selector switches 50 and to transmit sequence97, he will place contacts 51 and 81 in the positions shown. The B+supply voltage is applied to the base of the transistor 121 as one inputto the AND circuit by virtue of the path defined by the contacts 51 and52.9 of the selector switch 50, the conductor 113, and the contacts112.9 and 111. There is also provided a path along the conductor 144 toapply the B+ supply voltage to the base of the transistor 142, as afirst input to the second AND circuit 140. Similarly, there is provideda path through the contacts 81 and 82.7, the resistor 91 in theelectronic switch 90.7, the conductor 133, and the contacts 132.7 and131 of the selector switch 130, to enable the 13+ voltage to be appliedto the base of the transistor 141 as a second input to the AND circuit140. The B+ supply voltage also is applied along the conductor by theresistor 123 'to the base of the transistor 122 as a second input to thefirst AND circuit 120.

The concurrence of the B+ supply voltages, which may be consideredenabling signals, at the two inputs of the AND circuit 120, causes bothtransistors 121 and 122 to conduct, thereby effectively grounding themovable contact 111 (except for the saturation of voltage of each of thetransistors which is 0.2 volts each or about 0.4 volts all together).This diverts the current from the transistors 62 and 66 in theelectronic switch 60.9 and through the transistors 121 and 12.2. In thisregard, it should be noted that about 0.4 volts is necessary between thecontact 111 and ground before the transistors 121 and 122 conduct,whereas the transistors in the electronic switch 60.9 will not conductuntil the voltage is about 1.8 volts (0.6 volts for each of thetransistors 62 and 66 and for the diode 64), whereby the transistors 62and 66 will not conduct if the contacts 111 and 112.9 are engaged.Accordingly, the tap 76.9 on the inductor 76 in the oscillator 70 willnot become grounded despite the placement of the selector switch 50 inits number 9 position.

Also, the concurrence of the B+ enabling signals, at the two inputs ofthe AND circuit 140, causes both transistors 141 and 142 to conduct,thereby effectively grounding the movable contact 131 (except for thesaturation of the voltage of the transistors which is about 0.4 volt).This diverts the current from the transistors 92 and 96 in theelectronic switch 90.7 and through the transistors 141 and 142. In thisregard, 0.4 volt is necessary between the contact 131 and ground beforeboth the transistors 141 and 142 conduct, whereas the transistors in theelectronic switch 90.7 will not conduct until the voltage is about 1.8volts (0.6 volt for each of the transistors 92 and 96 and for the diode94), whereby the transistors 92 and 96 will not conduct if the contacts131 and 132.7 are engaged. Accordingly, the tap 106.7 on the inductor106 in the oscillator 100 will not become grounded despite the placementof the selector switch 80 in its number 7 position.

Also, the conduction of the transistors 141 and 142 provides a path forcurrent flow from the B+ supply through the base-emitter junction of thetransistor 151 in the electronic switch 150 and through the resistor152, thereby to close the electronic switch 150 and enable current toflow through the emitter-collector of the transistor 151, through theresistor 154, the movable contact 161 of the selector switch 160, thestationary contact 162.2 along the conductor 163, through the resistor65 in the electronic switch 60.2, through the base-emitter junction ofthe transistor 66, thereby causing the latter to conduct. Thiseffectively grounds the tap 76.2 on the inductor 76 and places theportion above the tap in parallel with the capacitors 74 and 75, so thatthe control tone developed by the oscillator 70 would be the number 2tone, despite the number 9 selection made on the selector switch 50.

In addition, current flows from the B+ supply through the transistor 151in the electronic switch 150, through the resistor 155, through thecontacts 171 and 172.4, along the conductor 173, through the resistor 95in the electronic switch 90.4, and through the baseemitter junction ofthe transistor 96, thereby to render it conductive. Conduction of thetransistor 96 effectively grounds the tap 106.4 of the inductor 106causing the oscillator 100 to oscillate and produce the number 4 tone,despite the fact that the selector switch 80 was set to cause theoscillator 100 to produce the number 7 tone.

Thus, by setting the selector switches 1 10 and 130 on the sequence oftones to be replaced (sequence 97) and by setting the selector switches160 and 170 on the sequence of tones to be substituted (24), the tonesequence 24 will be produced when the selector switches 50 and 80 areadjusted to produce the sequence 97.

Turning now to FIG. 3, an alternative form of the invention is shown,wherein parts thereof corresponding to parts in the system shown in FIG.2 are labeled with the same reference numerals with a factor 200 addedthereto. There is provided a rotary selector switch 250 having a movablecontact 251 and ten stationary contacts 252.10.10, which contacts arerespectively coupled to ten electronic switches 260.10.l0. Eachelectronic switch includes a resistor 261 coupled between the associatedstationary contacts of the switch 250 and the base of an NPN transistor262, the collector of which is coupled to the B+ supply voltage. Aresistor 263 is coupled between the base of the transistor 262 andground reference potential. A diode 264 and a resistor 265 are coupledin series between the emitter of the transistor 262 and the base of asecond NPN transistor 266, the emitter of which is grounded and thecollector of which is coupled to an associated tap on the inductor 276.The inductor 276 corresponds to the inductor 76 shown in FIG. 2, and ispart of an oscillator (not shown) corresponding to the oscillator 70.Coupled to the associated tap is the collector of a third NPN transistor267, the emitter of which is grounded. Also shown in FIG. 3 is aselector switch 360 corresponding to the switch 160 in FIG. 2, andhaving a movable contact 361 and a set of ten stationary contacts362.10.10. The bases of the transistors 267 in the electronic switches260.10.10 are respectively coupled to the stationary contacts362.1-0.l0. It is understood that AND circuits such as the AND circuits120 and 140, an electronic switch such as the electronic switch 150, anaselector switch such as the selector switch 170, are also provided andconnected in a similar manner. In addition, there are provided aselector switch corresponding to the selector switch 80, and

electronic switches corresponding to the electronic switches 90.1-0.l0,each modified by the addition of a transistor corresponding to thetransistor 267. Finally, a second oscillator, such as the oscillator100, is provided.

In operation, when the movable arm 251 is placed in the position shown,current will flow to the transitors 262 and 266 in the electronic switch260.9, thereby to ground the tap 276.9, all in the manner previouslydescribed with respect to the embodiment of FIG. 2. However, assumingthe selector switches 110, 130, and 80 are in the positions shown inFIG. 2, the current will be diverted away from the electronic switch260.9 and, instead, current will flow through the contacts 361 and 362.2of the selector switch 360 to render conductive and transistor 267,thereby effectively grounding the tap 276.2 on the inductor 276. Asimilar mode of operation would hold true for the channel which controlsthe second tone. Thus, what has been provided is a pair of cascadedtransistors for selectively grounding the taps on the inductor 276 (orany other impedance capable of controlling the frequency of oscillator)plus a third transistor for controlling the selective grounding of thetaps when the tone substitution system is pro gramed to substitute asequence of tones.

Turning now to FIGS. 4 and 5, the details of a tone substitution systempermitting the substitution of more than one tone or sequence of toneswill be described. There is provided a rotary selector switch 400 havinga movable contact 401 and five fixed contacts 402.l0.5, which fixedcontacts are respectively connected to conductors 403.l0.5. In thespecific example being described, the first tone in the sequence oftones may have one of five difference frequencies. However, it is to beunderstood that the invention includes a system capable of selecting tenfrequencies such as is achieved by the system disclosed in FIG. 2 by theuse of a ten-position selector switch or, in fact, a system capable ofselecting any number of frequencies. Five electronic switches (ES)404.10.5 respectively have the inputs thereof coupled to the conductors403.1-0.5. Each electronic switch 404.10.5 may be of the same basicconstruction as the electronic switch 60.2 shown in FIG. 2. There isprovided a variable frequency oscillator 407 having five frequencydetermining elements 407.10.5, which elements may correspond to theportions of the inductor 76 defined by the various taps 76.10.10 in theoscillator of FIG. 2. Conductors 405.10.5 respectively couple theoutputs of the electronic switches 404.10.5 to the frequency determiningelements 407.l-0.5 in a fashion similar to that described with respectto the system of FIG. 2. Energization of one of the electronic switches404.10.5 produces an output signal on the associated conductor 405.ll0.5to couple the associated frequency determining element 407.10.5 into theoscillator 407.

There is also provided a rotary selector switch '410 having a movablecontact 411 and five fixed contacts 4l2.l-0.5, which fixed contacts arerespectively connected to conductors 4l3.10.5. In this instance, thesecond tone also has one of five different frequencies. However, it isto be understood that any number of frequencies is contemplated. Fiveelectronic switches (ES) 4l4.1-0.5 respectively have the inputs thereofcoupled to the conductors 4l3.10.5. Each electronic switch 4l4.10.5 isof the same basic construction such as electronic switch 90.4 shown inFIG. 2. There is provided a variable frequency oscillator 417 havingfive frequency determining elements 417.10.5, which elements maycorrespond to the portions of the inductor 106 defined by the varioustaps l06.10.10 in the oscillator 100 of FIG. 2. Conductors 415.1-0.5respectively couple the outputs of the electronic switches 414.l0.5 tothe frequency determining elements 4l7.1-0.5 in a fashion similar tothat described with respect to the system of FIG. 2. Energization of oneof the electronic switches 414.ll0.5 produces an output signal on theassociated conductor 415.10.5 to couple the associated frequencydetermining element 417.l-0.5 into the oscillator 417.

In operation, the user sets up the switches 400 and 410 to produce thedesired sequence of control tones, in this case the sequence being 13. Apath for current flow is provided from the B+ supply voltage through thecontacts 401 and 402.1, the conductor 403.1 to the electronic switch404.1 which is thereby energized to provide an output signal. The outputsignal is produced on the conductor 405.1 and connects the frequencydetermining element 407.1 in the oscillator 407. Similarly, a path isprovided from the B+ supply voltage through the contacts 411 and 412.3through the conductor 413.3 into the electronic switch 414.3, which isthereby energized to provide an output signal. The output signal whichappears on the conductor 415.3 connects the frequency determiningelement 417.3 into the oscillator 417 to cause the same to produce acorresponding control tone. The tones produced by the two oscillators407 and 417 may then be coupled to gated amplifiers such as those shownlabeled 33 and 34 in FIG. 1.

A rotary selector switch 420 has a movable contact 421 and a set of fivestationary contacts 422.1-0.5, which stationary contacts are coupledrespectively to the conductors 403.1-0.5. Similarly, the rotary selectorswitch 430 has a movable contact 431 and a set of five stationarycontacts 432.10.5 respectively connected to the conductors 413.l-0.5.The contacts 421 and 431 are both coupled to a pair of AND circuits 423and 433, which AND circuits may be respectively constructed like the ANDcircuits 120 and 140 in FIG. 2. The output of the AND circuit 433 iscoupled toan electronic switch, which in turn is coupled to the movablecontacts 441 and 451 respectively of a pair of rotary selector switches440 and 450. The rotary selector switch 440 has a set of five stationarycontacts 441.1-0.5 respectively connected to the conductors 408.10.5which in turn are coupled respectively to a second input of theelectronic switches 404.1-0.5.

The selector switch 450 also has a set of five station ary contacts452.1-0.5 respectively connected to conductors 418.1-0.5 which in turnare coupled to a second input respectively of the electronic switches418.l0.5. The switches 420, 430, 440, and 450, the AND circuits 423 and433, and the electronic switch 434 define a first tone substitutionnetwork 425, which is capable of substituting one sequence of tones fora sequence set up on the selector switches 400 and 410.

Specifically, since the contact 421 of the selector switch 420 engagesthe contact 422.1, a path for current flow is defined by the contacts401 and 402.1 of the selector switch 400, the conductor 403.1 and thecontacts 422.1 and 421 of the selector switch 420, and is applied as afirst input to the AND circuit 423 and also is applied as a first inputto the AND circuit 433. Similarly, since the contact 431 of the selectorswitch 430 engages the contact 432.3, a path for current flow is definedby the contacts 411 and 412.3 of the selector switch 410, the conductor413.3 and the contacts 432.3 and 431 of the selector switch 430 and isapplied as a second input to the AND circuit 423 and also is applied asa second input to the AND circuit 433.

The AND circuit 423, in a fashion similar to the mode of operation ofthe AND circuit of FIG. 2 defines a path to divert the current flow fromthe electronic switch 404.1, thereby to render the same inoperative.Similarly, the AND circuit 433 provides a path to divert current flowfrom the electronic switch 414.3, thereby rendering the sameinoperative. The output of the AND circuit 433 is applied to theelectronic switch 434 to render the same operative to couple the B+supply voltage through the contacts 441 and 442.3 of the selector switch440, along the conductor 408.3, as an input to the electronic switch404.3. The electronic switch is thereby rendered operative to couple thefrequency determining element 407.3 into the oscillator 407. Thefrequency of the control tone by the oscillator 407 will be determinedby the value of the frequency determining element 407.3. Similarly, theB+ supply voltage is coupled through the contacts 451 and 452.2 of theselector switch 450, along the conductor 418.2, as an input to theelectronic switch 414.2. The electronic switch is thereby renderedoperative to couple the frequency determining element 417.2 into theoscillating 417. The frequency of the control tone produced by theoscillator 417 will be determined by the value of the frequencydetermining element 417.2.

Thus, the selector switches 420 and 430 are set up to correspond to thetone sequence 13 to be replaced and the selector switches 440 and 450are set up on the sequence 32 to be substituted. Now, if the selectorswitches 400 and 410 are set up to transmit tone sequence 13, tonesequence 32 will be sent instead.

Turning specifically to FIG. 5, there is provided a second tonesubstitution 485 which has the same basic construction as the network425, whereby corresponding elements are labeled with the same referencenumerals but with the factor of 60 added thereto. Specifically, there isprovided a rotary selector switch 480 which has a movable contact 481and a set of five stationary contacts 482.l0.5 which stationary contactsare coupled respectively to the conductors 403.1-0.5. There is alsoprovided a rotary selector switch 390 which has a movable contact 491and a set of five stationary contacts 492.1-0.5 respectively connectedto the conductors 4l3.l-0.5. The contacts 481 and 491 are both coupledto AND circuits 483 and 493, which AND circuits may be respectivelyconstructed like the AND circuits 120 and in FIG. 2. The output of theAND circuit 493 is coupled to an electronic switch 494, which in turn iscoupled to the movable contacts 501 and 511 respectively of a pair ofrotary selector switches 500 and 510. The switch 500 has stationarycontacts 502.10.5 respectively connected to the conductors 408.1-0.5which in turn are coupled respectively to a second input of theelectronic switches 404.1-0.5. The selector switch 510 also has a set offive stationary contacts 512.l0.5 respectively connected to conductors418.10.5 which in turn are coupled to a second input respectively of theelectronic switches 414.1-0.5. The second tone substitution network 485is capable of substituting a sequence of tones for a second sequence setup on the selector switches 400 and 410.

In the system shown, there is provided a third tone substitution network535 having the same construction as the network 425, and, accordingly,the elements are labeled with corresponding numerals with a factor of110 added thereto. Specifically, a rotary selector switch 530 has amovable contact 531 and a set of five stationary contacts 53l.10.5,which stationary contacts are coupled respectively to the conductors4011-05. Similarly, the rotary selector switch 540 has a movable contact541 and a set of five stationary contacts 542.l0.5 respectivelyconnected to the conductors 4l3.l0.5. The contacts 531 and 541 are bothcoupled to a pair of AND circuits 533 and 543, which AND circuits may berespectively constructed like the AND circuits 120 and 140 in FIG. 2.The output of the AND circuits 543 is coupled to an electronic switch544, which in turn is coupled to the movable contacts 551 and 561respectively of a pair of rotary selector switches 550 and 560. Therotary selector switch 550 has a set of five stationary contacts 552.l0.5 respectively connected to the conductors 408.l-0.5 which in turn arecoupled respectively to a second input of the electronic switches404.10.5. The selector switch 560 also has a set of five stationarycontacts 562.l0.5 respectively connected to conductors 418. 10.5 whichin turn are coupled to the second input respectively of the electronicswitches 4l4.10.5.

Considering now the operation of the network 485, the selector switches480 and 490 have been set on a tone sequence 44 and the switches 500 and510 have been set on the tone sequence 24. Accordingly, placement of theselector switches 400 and 410 to transmit a tone sequence 44, that is,in positions corresponding to the positions of the selector switches 480and 490, the tone sequence 24 would be sent instead, which representsthe positions of the selector switches 500 and 510. It should be notedthat with the selector switches 400 and 410 in the positions shown, thatis, to transmit tone sequence 13, the network 485 will have no effectsince the selector switches 480 and 490 are set on the tone sequence 44.As explained previously, in order for the tones set up on the selectorswitches 500 and 510 to be substituted, the tone sequence on theselector switches 480 and 490 must match the tone sequence on theselector switches 400 and 410.

Similarly, the selector switches 530 and 540 have been set on a tonesequence and the switches 550 and 560 have been set on the tone sequence43. Accordingly, placement of the selector switches 400 and 410 totransmit the tone sequence 15, that is, in positions corresponding tothe positions of the selector switches 530 and 540, the tone sequence 43would be sent instead, which represents the positions of the selectorswitches 550 and 560. It should be noted that with the selector switches400 and 410 in the positions shown, that is, in tone sequence 13, thenetwork 535 will have no effect since the selector switches 530 and 540are set on the tone sequence 15. In order for the tones set up on theselector switches 550 and 56010 be substituted, the tone sequence on theselector switches 530 and 540 must match the tone sequence on theselector switches 400 and 410.

The dashed conductors between the networks 485 and 535 indicate the factthat any number of such networks may be utilized. In this embodiment,three such networks 425, 485, and 535 have been shown, whereby thetransmitter would be capable of substituting three tone sequences. Inother words, if the operator were to select tone sequence 13, then tonesequence 32 would be sent automatically by virtue of the setup of thefirst network 425; if the operator were to select tone sequence 44, thentone sequence 24 would be sent automatically by virtue of thearrangement of the second network 485; and, if the operator were to setup the selector switches 400 and 410 to transmit the tone sequence 15,then the tone sequence 43 would be send instead, in accordance with thesetup in the third network 535.

With five available frequencies for the first control tone and fiveavailable frequencies for the second control tone, 25 different tonesequences are available. If it is desired that the transmitter becompletely versatile and capable of simultaneously substituting allsequences, 25 substitution networks, such as the network 425, would beneeded.

The system above described has a variety of advantageous features.First, substitution of one sequence for another sequence of tonesinvolves merely setting several rotary selector switches which may bemounted on the front of the transmitter so as to be easily accessible tothe operator. No patch cords or the like are needed to make the changeto provide for substitution. Also, no sequences need be placed aside foruse as spares as is required in other presently available systems. Inother words, in a system having available tone sequences (10 first tonesand 10 second tones), 10 were put aside as spares so that, when areceiver became faulty, it would be turned in and the owner would begiven one of the spare receivers. If all the spares were being used atthe time so that no spare was available, although several day-to-dayreceivers were available, the individual could not be given a receiver.On the other hand, in the system as above described, there are noparticular spares set aside, but rather any of the 100 tone sequencesmay be utilized either for a spare or for a continuous-operationreceiver.

When a receiver which is faulty has been turned in for repair by anindividual, and he is given a replacement receiver, the transmitter isprogramed to transmit the tone sequence corresponding to his newreceiver in response to dialing a tone sequence corresponding to his oldnumber. There is no need to return the receiver to the individual whenit is repaired, which saves the individual a trip back to the repairshop. The faulty receiver which has been repaired is then usable itselfas a spare. Accordingly, a receiver, for example, responsive to thesequence 12 which becomes faulty, may be turned in for repairs. The useris given a receiver responsive to the sequence, for example, '28. Afterthe operator sets up the selector switches in any one of the unusednetworks 425, 485, 435, etc., persons "wanting to call the individualcan call his old number 12, yet be connected to him through his newnumber 28.

If such a system finds particular use in a hospital, where Dr. Joneshas, for example, No. 15, and Dr. Smith has No. 18, Dr. Smith couldtransfer his calls to Dr. Jones without apprising would-be callers, byhaving one of the substitution networks set up to substitute sequence 15for sequence 18. Thus, callers desirous of getting in touch with Dr.Smith would dial sequence {18,

but, by virute of the tone substitution system, the transmitter wouldautomatically send sequence 15. Also, Dr. White, who has, say, No. 28,could have his calls transferred to Dr. Jones. By virtue of the presentsystem, any number of calls may be rerouted to Dr. Jones, withoutaffecting Dr. Jones ability to receive calls specifically directed tohim. This latter feature results from the fact that the No. 15 sequencehas not been programed into the appropriate selector switches in any oneof the networks.

What has been described, therefore, is an improved tone substitutionsystem for use in a transmitter of a selective calling communicationsystem. Although preferred embodiments of the invention have beendescribed, it is understood that various changes and modifications canbe made therein without departing from the spirit and scope of theinvention, and it is intended that all such changes and modifications becovered as fall within the scope of the appended claims.

What is claimed is:

1. A tone substitution system for use in a transmitter including atleast one oscillator with frequency determining means therein forgenerating a control tone, said tone substitution system comprising aplurality of electronic switches for coupling selected portions of thefrequency determining means in circuit in the oscillator, a firstselector switch having a first contact coupled to an enabling signal anda plurality of second contacts respectively coupled to said electronicswitches, said first selector switch being movable to a selectedposition to couple the enabling signal to the associated electronicswitch, thereby to render said last-mentioned electronic switchoperative to couple the associated portion of the frequency determiningmeans in circuit in the oscillator, a second selector switch having afirst contact and a plurality of second contacts individually coupled tothe second contacts of said first selector switch, a third selectorswitch having a first contact coupled to the first contact of saidsecond selector switch and a plurality of second contacts respectivelycoupled back to said electronic switches, said first selector switchbeing movable to a position corresponding to a preselected position ofsaid second selector switch to complete a path for the enabling signalthrough said second and third selector switches to the one of saidelectronic switches corresponding to the position of said thirdelectronic switch, thereby to render said last-mentioned electronicswitch operative to couple the associated portion of the frequencydetermining means in circuit in the oscillator, means responsive to saidfirst and second selector switches being in corresponding positions todivert the enabling signal away from the electronic switch associatedwith the selected position of said first selector switch.

2. The tone substitution system set forth in claim 1, wherein thefrequency determining means includes an inductor having a plurality oftaps thereon, said electronic switches being respectively coupled tosaid taps.

3. The tone substitution system set forth in claim 1, and furthercomprising an additional electronic switch coupled between said secondand third selector switches, said additional electronic switch beingresponsive to said first and second selector switches being incorresponding positions to couple an enabling signal through said thirdselector switch to the electronic switch associated therewith.

4. The tone substitution system set forth in claim 1, wherein each ofsaid electronic switches includes a pair of cascaded transistors.

5. The tone substitution system set forth in claim 4, wherein the secondcontacts of said third selector switch are coupled to the junction ofthe transistors respectively in said electronic switches.

6. The tone substitution system set forth in claim 4, wherein saidelectronic switches respectively include third transistors respectivelycoupled to the associated portions of the frequency determining means,the second contacts of said third selector switch being respectivelycoupled to said third transistors for controlling the conductionthereof.

7. The tone substitution system set forth in claim 1, wherein theenabling signal is a DC voltage used in supplying power to thetransmitter.

8. The tone substitution system set forth in claim 1, wherein each ofsaid selector switches is a rotary switch having a plurality of secondcontacts which are stationary and a first contact which is movable.

9. A tone substitution system for use in a transmitter including firstand second oscillators respectively generating two control tones andrespectively including first and second impedance networks therein, saidtone substitution system comprising a plurality of first electronicswitches for coupling selected portions of the first impedance networkin circuit in the first oscillator, a first selector switch having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to said first electronic switches, saidfirst selector switch being placeable in a selected condition to couplethe enabling signal to the associated first electronic switch, therebyto render said lastmentioned electronic switch operative to couple theassociated portion of the first impedance network to the firstoscillator, a plurality of second electronic switches coupling selectedportions of the second impedance network in circuit in the secondoscillator, a second selector switch having a first contact coupled toan enabling signal and a plurality of second contacts respectivelycoupled to said second electronic switches, said second selector switchbeing placeable in a selected condition to couple the enabling signal tothe associated second electronic switch, thereby to render saidlast-mentioned electronic switch operative to couple the associatedimpedance portion in the second oscillator, a third selector switchhaving a first contact and a plurality of second contacts individuallycoupled to the second contacts of said first selector switch, a

fourth selector switch having a first contact and a plurality of secondcontacts respectively coupled to the second contacts of said secondselector switch, an AND circuit having a pair of inputs respectivelycoupled to the first contacts of said third and fourth selectorswitches, said first selector switch being placeable in a conditioncorresponding to a preselected condition of said third selector switchto complete a path for the enabling signal through said third selectorswitch to said AND circuit, said second selector switch being placeablein a condition corresponding to a preselected condition of said fourthselector switch to complete a path for the enabling signal through saidfourth selector switch to said AND circuit, said AND circuit beingresponsive to the application thereto of enabling signals from saidthird and fourth selector switches to provide an output signal, a fifthselector switch having a first contact coupled to the output of said ANDcircuit and a plurality of second contacts respectively coupled back tosaid first electronic switches, said fifth selector switch beingoperative to conduct said output signal to the one of said firstelectronic switches corresponding to the condition of said fifthselector switch, thereby to render said last-mentioned electronic switchoperative to couple the associated impedance portion to the firstoscillator, a sixth selector switch having a first contact coupled tothe output of said AND circuit and a plurality of second contactsrespectively coupled back to said second electronic switches, said sixthselector switch being operative to conduct said output signal to the oneof said second electronic switches corresponding to the condition ofsaid sixth selector switch, thereby to render said last-mentionedelectronic switch operative to couple the associated impedance portionto the second oscillator, means responsive to said first and thirdselector switches being in corresponding conditions and said second andfourth selector switches being in corresponding conditions to divert theenabling signals away from the electronic switches associated with theselected conditions of said first and second selector switches.

10. The tone substitution system set forth in claim 9, wherein said ANDcircuit includes a pair of transistors connected in series, the firstcontact of said third selector switch being coupled to the input of oneof said transistors and the first contact of said fourth selector switchbeing coupled to the input of the other of said transistors.

11. The tone substitution system set forth in claim 9, wherein said ANDcircuit is operative to divert the enabling signal from the firstelectronic switches when said first and third selector switches are incorresponding conditions, and further comprising a second AND circuitfor diverting the enabling signal from said second electronic switcheswhen said second and fourth selector switches are in correspondingconditions.

12. A tone substitution system for use in a transmitter including firstand second oscillators respectively gen erating two control tones andrespectively including first and second impedance networks therein, saidtone substitution system comprising a plurality of first electronicswitches for coupling selected portions of the first impedance networkin circuit in the first oscillator, a first selector switch having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to said first electronic switches, saidfirst selector switch being placeable in a selected condition to couplethe enabling signal to the associated first electronic switch, therebyto render said lastmentioned electronic switch operative to couple theassociated portion of the first impedance to the first oscillator, aplurality of second electronic switches respectively coupling selectedportions of the second impedance network in circuit in the secondoscillator, a second selector switch having a first contact coupled toan enabling signal and a plurality of second contacts respectivelycoupled to said second electronic switches, said second selector switchbeing placeable in a selected condition to couple the enabling signal tothe associated second electronic switch, thereby to render saidlast-mentioned electronic switch operative to couple the associatedimpedance portion in the second oscillator, a third selector switchhaving a first contact and a plurality of second contacts individuallycoupled to the second contacts of said first selector switch, a fourthselector switch having a first contact and a plurality of secondcontacts respectively coupled to the second contacts of said secondselector switch, a pair of AND circuits each having a pair of inputsrespectively coupled to the first contacts of said third and fourthselector switches, said first selector switch being placeable in acondition corresponding to a preselected condition of said thirdselector switch to complete a path for the enabling signal through saidthird selector switch to said AND circuits, said second selector switchbeing placeable in a condition corresponding to a preselected conditionof said fourth selector switch to complete a path for the enablingsignal through said fourth selector switch to said AND circuits, one ofsaid AND circuits being responsive to the application thereto ofenabling signals from said third and fourth selector switches to providean output signal, a fifth selector switch having a first contact coupledto the output of said one AND circuit and a plurality of second contactsrespectively coupled back to said first electronic switches, said fifthselector switch being operative to conduct said output signal to the oneof said first electronic switches corresponding to the condition of saidfifth selector switch, thereby to render said lastmentioned electronicswitch operative to couple the associated impedance portion to the firstoscillator, a sixth selector switch having a first contact coupled tothe output of said one AND circuit and a plurality of second contactsrespectively coupled back to said second electronic switches, said sixthselector switch being operative to conduct said output signal to the oneof said second electronic switches corresponding to the condition ofsaid sixth selector switch, thereby to render said last-mentionedelectronic switch operative to couple the associated impedance portionto the second oscillator, one of said AND circuits including meansresponsive to said first and third selector switches being incorresponding conditions to divert the enabling signals away from theelectronic switch associated with the selected condition of said firstselector switch, the other of said AND circuits including meansresponsive to said second and fourth selector switches being incorresponding conditions to divert the enabling signals away from theelectronic switch associated with theselected conditions of said secondselector switch.

13. A tone substitution system for use in a transmitter including atleast one oscillator for generating a control tone and including animpedance network, said tone substitution system comprising a pluralityof electronic switches for coupling selected portions of the impedancenetwork in circuit in the oscillator, a first selector switch having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to said electronic switches, said firstselector switch being placeable in a selected condition to couple theenabling signal to the associated electronic switch, thereby to rendersaid last-mentioned electronic switch operative to couple the associatedfrequency determining element to the oscillator, a plurality of secondselector switches each having a first contact and a plurality of secondcontacts individually coupled to the second contacts of said firstselector switch, a plurality of third switches each having a firstcontact coupled to the first contact of an associated second selectorswitch and a plurality of second contacts respectively coupled back tosaid electronic switches, said first selector switch being placeable ina condition corresponding to a preselected condition of any of saidsecond selector switches to complete a path for the enabling signalthrough said last-mentioned second selector switch and through theassociated third selector switch to the one of said electronic switchescorresponding to the condition of said last-mentioned third selectorswitch, thereby to render said last-mentioned electronic switchoperative to couple the associated impedance portion to the oscillator,means responsive to said first and second selector switches being incorresponding conditions to divert the enabling signal away from theelectronic switch associated with the selected condition of said firstselector switch.

14. The tone substitution system set forth in claim 13, wherein thereare as many second selector switches and there are as many thirdselector switches as there are impedance portions, whereby any desirednumber of control tones may be substituted.

15. A tone substitution system for use in a transmitter including aplurality of oscillators respectively generating a plurality of controltones and each having an impedance network, said tone substitutionsystem comprising a plurality of sets of electronic switchesrespectively coupling portions of the impedance networks respectively tothe oscillators, a plurality of first selector switches each having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to the electronic switches in a set ofelectronic switches, each of said first selector switches beingplaceable in a selected condition to couple the enabling signal to theassociated electronic switch, thereby to render said last-mentionedelectronic switch operative to couple the associated impedance portionto the associated oscillator, a plurality of second selector switcheseach having a first contact and a plurality of second contactsrespectively coupled to the second contacts of said first selectorswitches, an AND circuit having a plurality of inputs respectivelycoupled to the first contacts of said second selector switches, each ofsaid first selector switches being placeable in a conditioncorresponding to a preselected condition of the associated secondselector switch to complete a path for the enabling signal through theassociated second selector switch to said AND circuit, a plurality ofthird selector switches each having a first contact coupled to theoutput of said AND circuit and a plurality of second contactsrespectively coupled to the associated second electronic switches, eachof said third selector switches being operative to conduct said outputsignal to the electronic switch corresponding to the condition of saidthird selector switch, thereby to render said lastmentioned electronicswitch operative to couple the associated impedance portion in theassociated oscillator, means responsive to associated first and secondselector switches being in corresponding conditions to divert theenabling signals away from the electronic switches associated with theselected conditions of said first selector switches.

16. A tone substitution system for use in a transmitter and comprisingtone signal producing means, first selector means coupled to said tonesignal producing means and placeable in one of a plurality of conditionsto cause the tone signal to have a selected one of a correspondingplurality of first characteristics, second selector means coupled tosaid tone signal producing means and placeable in one of a plurality ofconditions to cause the tone signal to have a selected one of acorresponding plurality of second characteristics, and third selectormeans coupled to said first and second selector means and placeable inone of a plurality of conditions for rendering said first selector meansor said second selector means operative to control the characteristicsof the tone signal, the tone signal having the selected one of saidfirst characteristics when the conditions of said first and thirdselector means do not correspond, the tone signal having the selectedone of said second characteristics when the conditions of said first andthird selector means correspond.

17. The tone substitution system set forth in claim 16, wherein saidtone signal producing means includes at least one variable frequencyoscillator for providing a plurality of control tones respectivelyhaving frequencies corresponding to the plurality of conditions of saidfirst selector means.

18. The tone substitution system set forth in claim 16, wherein each ofsaid selector means includes a manually operable multi-position selectorswitch.

19. The tone substitution system set forth in claim 16, wherein saidtone signal producing means includes at least two variable frequencyoscillators for providing two control tones, the frequencies of saidcontrol tones being determined by the conditions of said selector means.

20. The tone substitution system set forth in claim 16, wherein saidtone signal producing means includes a variable frequency oscillatorhaving an impedance network, portions of said network being adapted tobe individually coupled in circuit in said oscillator, and furthercomprising electronic switching means coupled to said impedance networkportions for respective switching thereof into and out of circuit insaid oscillator, said first and second selector means being coupled tosaid electronic switching means for controlling the switching thereof.

21. The tone substitution system set forth in claim 16, and furthercomprising a plurality of electronic switching means having inputscoupled to said first selector means and having outputs coupled to saidsecond selector means and having outputs coupled to said tone signalproducing means.

22. A tone substitution system for use in a transmitter and comprising anumber of variable frequency oscillators for producing control tones, anumber of first selector means respectively coupled to said oscillatorsand each being placeable in one of a plurality of conditions to causethe associated control tone to have a selected one of a correspondingplurality of first frequencies, a number of second selector meansrespectively coupled to said oscillators and each being placeable in oneof a plurality of conditions to cause the associated control tone tohave a selected one of a corresponding plurality of second frequencies,a number of third selector means respectively coupled to the associatedpairs of said first and second selector means and being placeable in oneof a plurality of conditions for causing the frequency of the associatedcontrol tone to be controlled by the associated first selector means orthe associated second selector means, each control tone having theassociated selected one of said first frequencies when the conditions ofthe associated first and third selector means do not correspond, eachcontrol tone having the associated selected one of said secondfrequenhaving inputs respectively coupled to said third selector meansand to said first selector means, each of said AND circuits beingoperative to produce an output signal only when each associated pair offirst and third selector means is in corresponding conditions, each ofsaid second selector means being respectively coupled to said ANDcircuit and responsive to said output signals to control the frequenciesof the control tones produced by said oscillators.

24. The tone substitution system set forth in claim 22, wherein each ofsaid variable frequency oscillators includes impedance network portionswhich may individually be coupled in circuit in the associatedoscillator, and further comprising a plurality of electronic switchingmeans respectively coupled to said impedance network portions forrespective switching thereof into and out of circuit with the associatedoscillators, associated pairs of said first and second selector meansbeing respectively coupled to the associated electronic switching meansfor controlling the switching thereof.

25. A tone substitution system for use in a transmitter and comprisingat least two variable frequency oscillators for producing a pair ofcontrol tones, at least two first selector means respectively coupled tosaid oscillators and each being placeable in one of a plurality ofconditions to cause the associated control tone to have a selected oneof a corresponding plurality of first frequencies, at least two secondselector means respectively coupled to said oscillators and each beingplaceable in one of a plurality of conditions to cause the associatedcontrol tone to have a selected one of a corresponding plurality ofsecond frequencies, at least two third selector means respectivelycoupled to the associated pairs of said first and second selector meansand being placeable in one of a plurality of conditions for causing thefrequency of the associated control tone to be controlled by theassociated first selector means or the associated second selector means,each control tone having the associated selected one of said firstfrequencies when the conditions of the associated first and thirdselector means do not correspond, each control tone having theassociated selected one of said second frequencies when the conditionsof the associated first and third selector means correspond.

26. The tone substitution system set forth in claim 25, and furthercomprising an AND circuit having inputs coupled to each of said firstselector means and to each of said third selector means and operative toproduce an output signal only when each associated pair of first andthird selector means is in corresponding conditions, each of said secondselector means being coupled to said AND circuit and responsive to saidoutput signals to control the frequencies of the control tones producedby said oscillators.

27. A tone substitution system for use in a transmitter and comprisingtone signal producing means, first selector means coupled to said tonesignal producing means and being placeable in one of a plurality ofconditions to cause the tone signal to have a selected one of acorresponding plurality of first characteristics, a plurality of secondselector means coupled to said tone signal producing means and eachbeing placeable in one of a plurality of conditions to cause the tonesignal to have a selected one of a corresponding plurality of secondcharacteristics, and a plurality of third selector means coupled to saidfirst selector means and respectively coupled to said plurality ofsecond selector means, each of said third selector means being placeablein one of a plurality of conditions for rendering said first selectormeans or the associated one of said second selector means operative tocontrol the characteristics of the tone signal, when the condition ofnone of said third selector means corresponds to the condition of saidfirst selector means the tone signal has the selected one of said firstcharacteristics, when the condition of one of said third selector meanscorresponds to the condition of said first selector means the tonesignal has the one of said second characteristics associated with theone of said second selector means coupled to said one third selectormeans.

28. The tone substitution system set forth in claim 27, wherein thenumber of second selector means equals the number of third selectormeans.

29. The tone substitution system set forth in claim 27, wherein thenumber of second selector means is the same as the number of thirdselector means and is no less than the number of said firstcharacteristics.

30. The tone substitution system set forth in claim 27, wherein saidtone signal producing means includes at least two variable frequencyoscillators for providing two control tones, the frequencies of saidcontrol tones being determined by the conditions 'of said selectormeans.

31. The tone substitution system set forth in claim 27, and furthercomprising a plurality of electronic switching means having inputscoupled to said first selector means, having inputs coupled to saidplurality of second selector means and having outputs coupled to saidtone signal producing means.

32. A signal substitution system for use in a transmitter including atone generator for generating at least one tone having a frequencyselected from a plurality of possible frequencies, and comprisingprimary-tone selecting means coupled to the tone generator and placeablein a plurality of conditions to cause the tone produced by the tonegenerator to have a given frequency, substituting means coupled to saidprimarytone selecting means and being placeable in a plurality ofconditions corresponding to the conditions of at least some of theconditions of said primary-tone selecting means, said substituting meansproviding an output when the condition thereof corresponds to thecondition of said primary-tone selecting means, and substitute-toneselecting means coupled to the tone generator and placeable in aplurality of conditions to cause the tone produced by the tone generatorto have a different frequency, said substitute-tone selecting meansbeing coupled to said substituting means and responsive to the outputtherefrom to cause the tone generator to produce the tone having saiddifferent frequency instead of the tone having said given frequency.

33. The signal substitution system set forth in claim 32, and furthercomprising electronic switching means coupled between said primary-toneselecting means means and being operative to cause the tone generator toproduce a tone having said difference frequency in accordance with thecondition of said substitute-tone selecting means.

34. The signal substitution system set forth in claim 32, wherein saidprimary-tone selecting means includes a multiposition manual switch.

35. A signal substitution system for use in a transmitter including atone generator for generating a plurality of tones respectively havingfrequencies selected from a plurality of possible frequencies, andcomprising a plurality of primary-tone selecting means coupled to thetone generator and each placeable in a plurality of conditions to causethe tones produced by the tone generator respectively to have givenfrequencies, a plurality of substituting means respectively coupled tosaid plurality of primary-tone selecting means and each placeable in aplurality of conditions corresponding to the conditions of at least someof the conditions of the associated primary-tone selecting means, eachof said substituting means providing a signal when the condition thereofcorresponds to the condition of the associated one of said primary-toneselecting means, AND circuit means coupled to said plurality ofsubstituting means and responsive to the concurrence of a signal fromeach of said substituting means to provide an output, and a plurality ofsubstitute-tone selecting means coupled to the tone generator and eachplaceable in a plurality of conditions to cause the tones produced bythe tone generator respectively to have different frequencies, each ofsaid substitute-tone selecting means being coupled to said AND circuitmeans and responsive to the output therefrom to cause the tone generatorto produce the tones having said different frequencies instead of thetones having said given frequencies.

36. A signal substitution system for use in a transmitter including atone generator for generating at least one tone having a frequencyselected from a plurality of possible frequencies, and a primary-toneselector placeable in a plurality of conditions to cause the toneproduced by the tone generator to have a given frequency, said signalsubstitution system comprising substituting means for coupling to theprimary-tone selector and being placeable in a plurality of conditionscorresponding to the conditions of at least some of the conditions ofthe primary-tone selector, said substituting means providing an outputwhen the condition thereof corresponds to the condition of theprimarytone selector, and substitute-tone selecting means for operatingthe tone generator and placeable in a plurality of conditions to causethe tone produced by the tone generator to have a different frequency,said substitutetone selecting means being coupled to said substitutingmeans and responsive to the output therefrom to cause the tone generatorto produce the tone having said different frequency instead of the tonehaving said given frequency.

37. The signal substitution system set forth in claim 36, and furthercomprising electronic switching means for coupling between theprimary-tone selector and the tone generator and being operative tocause the tone generator to produce a tone having the given frequency inaccordance with the condition of the primary-tone selector, saidsubstitute-tone selecting means being coupled to said electronicswitching means and being operative to cause the tone generator toproduce a tone having said different frequency in accordance with thecondition of said substitute-tone selecting means.

38. a signal substitution system for use in a transmitter including atone generator for generating a plurality of tones respectively havingfrequencies selected from a plurality of possible frequencies and aplurality of primary-tone selectors each placeable in a plurality ofconditions to cause the tones produced by the tone generatorrespectively to have given frequencies, said signal substitution systemcomprising a plurality of substituting means for respectively couplingto the primary-tone selectors and each placeable in a plurality of 7conditions corresponding to the conditions of at least some of theconditions of the associated primary-tone selectors, each of saidsubstituting means providing a signal when the condition thereofcorresponds to the condition of the associated one of the primary-toneselectors, AND circuit means coupled to said plurality of substitutingmeans and responsive to the concurrence of a signal from each of saidsubstituting means to provide an output, and a plurality ofsubstitute-tone selecting means for coupling to the tone generator andeach placeable in a plurality of conditions to cause the tones producedby the tone generator respectively to have difference frequenceis, eachof said substitute-tone selecting means being coupled to said ANDcircuit means and responsive to the output therefrom to cause the tonegenerator to produce the tones having said different frequencies insteadof the tones having said given frequencies.

1. A tone substitution system for use in a transmitter including atleast one oscillator with frequency determining means therein forgenerating a control tone, said tone substitution system comprising aplurality of electronic switches for coupling selected portions of thefrequency determining means in circuit in the oscillator, a firstselector switch having a first contact coupled to an enabling signal anda plurality of second contacts respectively coupled to said electronicswitches, said first selector switch being movable to a selectedposition to couple the enabling signal to the associated electronicswitch, thereby to render said last-mentioned electronic switchoperative to couple the associated portion of the frequency determiningmeans in circuit in the oscillator, a second selector switch having afirst contact and a plurality of second contacts individually coupled tothe second contacts of said first selector switch, a third selectorswitch having a first contact coupled to the first contact of saidsecond selector switch and a plurality of second contacts respectivelycoupled back to said electronic switches, said first selector switchbeing movable to a position corresponding to a preselected position ofsaid second selector switch to complete a path for the enabling signalthrough said second and third selector switches to the one of saidelectronic switches corresponding to the position of said thirdelectronic switch, thereby to render said last-mentioned electronicswitch operative to couple the associated portion of the frequencydetermining means in circuit in the oscillator, means responsive to saidfirst and second selector switches being in corresponding positions todivert the enabling signal away from the electronic switch associatedwith the selected position of said first selector switch.
 2. The tonesubstitution system set forth in claim 1, wherein the frequencydetermining means includes an inductor having a plurality of tapsthereon, said electronic switches being respectively coupled to saidtaps.
 3. The tone substitution system set forth in claim 1, and furthercomprising an additional electronic switch coupled between said secondand third selector switches, said additional electronic switch beingresponsive to said first and second selector switches being incorresponding positions to couple an enabling signal through said thirdselector switch to the electronic switch associated therewith.
 4. Thetone substitution system set forth in claim 1, wherein each of saidelectronic switches includes a pair of cascaded transistors.
 5. The tonesubstitution system set forth in claim 4, wherein the second contacts ofsaid third selector switch are coupled to the junction of thetransistors respectively in said electronic switches.
 6. The tonesubstitution system set forth in claim 4, wherein said electronicswitches respectively include third transistors respectively coupled tothe associated portions of the frequency determining means, the secondcontacts of said third selector switch being respectively coupled tosaid third transistors for controlling the conduction thereof.
 7. Thetone substitution system set forth in claim 1, wherein the enablingsignal is a DC voltage used in supplying power to the transmitter. 8.The tone substitution system set forth in claim 1, wherein each of saidselector switches is a rotary switch having a plurality of secondcontacts which are stationary and a first contact which is movable.
 9. Atone substitution system for use in a transmitter including first andsecond oscillators respectively generating two control tones andrespectively including first and second impedance nEtworks therein, saidtone substitution system comprising a plurality of first electronicswitches for coupling selected portions of the first impedance networkin circuit in the first oscillator, a first selector switch having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to said first electronic switches, saidfirst selector switch being placeable in a selected condition to couplethe enabling signal to the associated first electronic switch, therebyto render said last-mentioned electronic switch operative to couple theassociated portion of the first impedance network to the firstoscillator, a plurality of second electronic switches coupling selectedportions of the second impedance network in circuit in the secondoscillator, a second selector switch having a first contact coupled toan enabling signal and a plurality of second contacts respectivelycoupled to said second electronic switches, said second selector switchbeing placeable in a selected condition to couple the enabling signal tothe associated second electronic switch, thereby to render saidlast-mentioned electronic switch operative to couple the associatedimpedance portion in the second oscillator, a third selector switchhaving a first contact and a plurality of second contacts individuallycoupled to the second contacts of said first selector switch, a fourthselector switch having a first contact and a plurality of secondcontacts respectively coupled to the second contacts of said secondselector switch, an AND circuit having a pair of inputs respectivelycoupled to the first contacts of said third and fourth selectorswitches, said first selector switch being placeable in a conditioncorresponding to a preselected condition of said third selector switchto complete a path for the enabling signal through said third selectorswitch to said AND circuit, said second selector switch being placeablein a condition corresponding to a preselected condition of said fourthselector switch to complete a path for the enabling signal through saidfourth selector switch to said AND circuit, said AND circuit beingresponsive to the application thereto of enabling signals from saidthird and fourth selector switches to provide an output signal, a fifthselector switch having a first contact coupled to the output of said ANDcircuit and a plurality of second contacts respectively coupled back tosaid first electronic switches, said fifth selector switch beingoperative to conduct said output signal to the one of said firstelectronic switches corresponding to the condition of said fifthselector switch, thereby to render said last-mentioned electronic switchoperative to couple the associated impedance portion to the firstoscillator, a sixth selector switch having a first contact coupled tothe output of said AND circuit and a plurality of second contactsrespectively coupled back to said second electronic switches, said sixthselector switch being operative to conduct said output signal to the oneof said second electronic switches corresponding to the condition ofsaid sixth selector switch, thereby to render said last-mentionedelectronic switch operative to couple the associated impedance portionto the second oscillator, means responsive to said first and thirdselector switches being in corresponding conditions and said second andfourth selector switches being in corresponding conditions to divert theenabling signals away from the electronic switches associated with theselected conditions of said first and second selector switches.
 10. Thetone substitution system set forth in claim 9, wherein said AND circuitincludes a pair of transistors connected in series, the first contact ofsaid third selector switch being coupled to the input of one of saidtransistors and the first contact of said fourth selector switch beingcoupled to the input of the other of said transistors.
 11. The tonesubstitution system set forth in claim 9, wheRein said AND circuit isoperative to divert the enabling signal from the first electronicswitches when said first and third selector switches are incorresponding conditions, and further comprising a second AND circuitfor diverting the enabling signal from said second electronic switcheswhen said second and fourth selector switches are in correspondingconditions.
 12. A tone substitution system for use in a transmitterincluding first and second oscillators respectively generating twocontrol tones and respectively including first and second impedancenetworks therein, said tone substitution system comprising a pluralityof first electronic switches for coupling selected portions of the firstimpedance network in circuit in the first oscillator, a first selectorswitch having a first contact coupled to an enabling signal and aplurality of second contacts respectively coupled to said firstelectronic switches, said first selector switch being placeable in aselected condition to couple the enabling signal to the associated firstelectronic switch, thereby to render said last-mentioned electronicswitch operative to couple the associated portion of the first impedanceto the first oscillator, a plurality of second electronic switchesrespectively coupling selected portions of the second impedance networkin circuit in the second oscillator, a second selector switch having afirst contact coupled to an enabling signal and a plurality of secondcontacts respectively coupled to said second electronic switches, saidsecond selector switch being placeable in a selected condition to couplethe enabling signal to the associated second electronic switch, therebyto render said last-mentioned electronic switch operative to couple theassociated impedance portion in the second oscillator, a third selectorswitch having a first contact and a plurality of second contactsindividually coupled to the second contacts of said first selectorswitch, a fourth selector switch having a first contact and a pluralityof second contacts respectively coupled to the second contacts of saidsecond selector switch, a pair of AND circuits each having a pair ofinputs respectively coupled to the first contacts of said third andfourth selector switches, said first selector switch being placeable ina condition corresponding to a preselected condition of said thirdselector switch to complete a path for the enabling signal through saidthird selector switch to said AND circuits, said second selector switchbeing placeable in a condition corresponding to a preselected conditionof said fourth selector switch to complete a path for the enablingsignal through said fourth selector switch to said AND circuits, one ofsaid AND circuits being responsive to the application thereto ofenabling signals from said third and fourth selector switches to providean output signal, a fifth selector switch having a first contact coupledto the output of said one AND circuit and a plurality of second contactsrespectively coupled back to said first electronic switches, said fifthselector switch being operative to conduct said output signal to the oneof said first electronic switches corresponding to the condition of saidfifth selector switch, thereby to render said last-mentioned electronicswitch operative to couple the associated impedance portion to the firstoscillator, a sixth selector switch having a first contact coupled tothe output of said one AND circuit and a plurality of second contactsrespectively coupled back to said second electronic switches, said sixthselector switch being operative to conduct said output signal to the oneof said second electronic switches corresponding to the condition ofsaid sixth selector switch, thereby to render said last-mentionedelectronic switch operative to couple the associated impedance portionto the second oscillator, one of said AND circuits including meansresponsive to said first and third selector switches being incorresponding conditions to divErt the enabling signals away from theelectronic switch associated with the selected condition of said firstselector switch, the other of said AND circuits including meansresponsive to said second and fourth selector switches being incorresponding conditions to divert the enabling signals away from theelectronic switch associated with the selected conditions of said secondselector switch.
 13. A tone substitution system for use in a transmitterincluding at least one oscillator for generating a control tone andincluding an impedance network, said tone substitution system comprisinga plurality of electronic switches for coupling selected portions of theimpedance network in circuit in the oscillator, a first selector switchhaving a first contact coupled to an enabling signal and a plurality ofsecond contacts respectively coupled to said electronic switches, saidfirst selector switch being placeable in a selected condition to couplethe enabling signal to the associated electronic switch, thereby torender said last-mentioned electronic switch operative to couple theassociated frequency determining element to the oscillator, a pluralityof second selector switches each having a first contact and a pluralityof second contacts individually coupled to the second contacts of saidfirst selector switch, a plurality of third switches each having a firstcontact coupled to the first contact of an associated second selectorswitch and a plurality of second contacts respectively coupled back tosaid electronic switches, said first selector switch being placeable ina condition corresponding to a preselected condition of any of saidsecond selector switches to complete a path for the enabling signalthrough said last-mentioned second selector switch and through theassociated third selector switch to the one of said electronic switchescorresponding to the condition of said last-mentioned third selectorswitch, thereby to render said last-mentioned electronic switchoperative to couple the associated impedance portion to the oscillator,means responsive to said first and second selector switches being incorresponding conditions to divert the enabling signal away from theelectronic switch associated with the selected condition of said firstselector switch.
 14. The tone substitution system set forth in claim 13,wherein there are as many second selector switches and there are as manythird selector switches as there are impedance portions, whereby anydesired number of control tones may be substituted.
 15. A tonesubstitution system for use in a transmitter including a plurality ofoscillators respectively generating a plurality of control tones andeach having an impedance network, said tone substitution systemcomprising a plurality of sets of electronic switches respectivelycoupling portions of the impedance networks respectively to theoscillators, a plurality of first selector switches each having a firstcontact coupled to an enabling signal and a plurality of second contactsrespectively coupled to the electronic switches in a set of electronicswitches, each of said first selector switches being placeable in aselected condition to couple the enabling signal to the associatedelectronic switch, thereby to render said last-mentioned electronicswitch operative to couple the associated impedance portion to theassociated oscillator, a plurality of second selector switches eachhaving a first contact and a plurality of second contacts respectivelycoupled to the second contacts of said first selector switches, an ANDcircuit having a plurality of inputs respectively coupled to the firstcontacts of said second selector switches, each of said first selectorswitches being placeable in a condition corresponding to a preselectedcondition of the associated second selector switch to complete a pathfor the enabling signal through the associated second selector switch tosaid AND circuit, a plurality of third selector switches each having afirst contact couPled to the output of said AND circuit and a pluralityof second contacts respectively coupled to the associated secondelectronic switches, each of said third selector switches beingoperative to conduct said output signal to the electronic switchcorresponding to the condition of said third selector switch, thereby torender said last-mentioned electronic switch operative to couple theassociated impedance portion in the associated oscillator, meansresponsive to associated first and second selector switches being incorresponding conditions to divert the enabling signals away from theelectronic switches associated with the selected conditions of saidfirst selector switches.
 16. A tone substitution system for use in atransmitter and comprising tone signal producing means, first selectormeans coupled to said tone signal producing means and placeable in oneof a plurality of conditions to cause the tone signal to have a selectedone of a corresponding plurality of first characteristics, secondselector means coupled to said tone signal producing means and placeablein one of a plurality of conditions to cause the tone signal to have aselected one of a corresponding plurality of second characteristics, andthird selector means coupled to said first and second selector means andplaceable in one of a plurality of conditions for rendering said firstselector means or said second selector means operative to control thecharacteristics of the tone signal, the tone signal having the selectedone of said first characteristics when the conditions of said first andthird selector means do not correspond, the tone signal having theselected one of said second characteristics when the conditions of saidfirst and third selector means correspond.
 17. The tone substitutionsystem set forth in claim 16, wherein said tone signal producing meansincludes at least one variable frequency oscillator for providing aplurality of control tones respectively having frequencies correspondingto the plurality of conditions of said first selector means.
 18. Thetone substitution system set forth in claim 16, wherein each of saidselector means includes a manually operable multi-position selectorswitch.
 19. The tone substitution system set forth in claim 16, whereinsaid tone signal producing means includes at least two variablefrequency oscillators for providing two control tones, the frequenciesof said control tones being determined by the conditions of saidselector means.
 20. The tone substitution system set forth in claim 16,wherein said tone signal producing means includes a variable frequencyoscillator having an impedance network, portions of said network beingadapted to be individually coupled in circuit in said oscillator, andfurther comprising electronic switching means coupled to said impedancenetwork portions for respective switching thereof into and out ofcircuit in said oscillator, said first and second selector means beingcoupled to said electronic switching means for controlling the switchingthereof.
 21. The tone substitution system set forth in claim 16, andfurther comprising a plurality of electronic switching means havinginputs coupled to said first selector means and having outputs coupledto said second selector means and having outputs coupled to said tonesignal producing means.
 22. A tone substitution system for use in atransmitter and comprising a number of variable frequency oscillatorsfor producing control tones, a number of first selector meansrespectively coupled to said oscillators and each being placeable in oneof a plurality of conditions to cause the associated control tone tohave a selected one of a corresponding plurality of first frequencies, anumber of second selector means respectively coupled to said oscillatorsand each being placeable in one of a plurality of conditions to causethe associated control tone to have a selected one of a correspondingplurality of second frequencies, a number of third selector meansreSpectively coupled to the associated pairs of said first and secondselector means and being placeable in one of a plurality of conditionsfor causing the frequency of the associated control tone to becontrolled by the associated first selector means or the associatedsecond selector means, each control tone having the associated selectedone of said first frequencies when the conditions of the associatedfirst and third selector means do not correspond, each control tonehaving the associated selected one of said second frequencies when theconditions of the associated first and third selector means correspond.23. The tone substitution system set forth in claim 22, and furthercomprising a number of AND circuits each having inputs respectivelycoupled to said third selector means and to said first selector means,each of said AND circuits being operative to produce an output signalonly when each associated pair of first and third selector means is incorresponding conditions, each of said second selector means beingrespectively coupled to said AND circuit and responsive to said outputsignals to control the frequencies of the control tones produced by saidoscillators.
 24. The tone substitution system set forth in claim 22,wherein each of said variable frequency oscillators includes impedancenetwork portions which may individually be coupled in circuit in theassociated oscillator, and further comprising a plurality of electronicswitching means respectively coupled to said impedance network portionsfor respective switching thereof into and out of circuit with theassociated oscillators, associated pairs of said first and secondselector means being respectively coupled to the associated electronicswitching means for controlling the switching thereof.
 25. A tonesubstitution system for use in a transmitter and comprising at least twovariable frequency oscillators for producing a pair of control tones, atleast two first selector means respectively coupled to said oscillatorsand each being placeable in one of a plurality of conditions to causethe associated control tone to have a selected one of a correspondingplurality of first frequencies, at least two second selector meansrespectively coupled to said oscillators and each being placeable in oneof a plurality of conditions to cause the associated control tone tohave a selected one of a corresponding plurality of second frequencies,at least two third selector means respectively coupled to the associatedpairs of said first and second selector means and being placeable in oneof a plurality of conditions for causing the frequency of the associatedcontrol tone to be controlled by the associated first selector means orthe associated second selector means, each control tone having theassociated selected one of said first frequencies when the conditions ofthe associated first and third selector means do not correspond, eachcontrol tone having the associated selected one of said secondfrequencies when the conditions of the associated first and thirdselector means correspond.
 26. The tone substitution system set forth inclaim 25, and further comprising an AND circuit having inputs coupled toeach of said first selector means and to each of said third selectormeans and operative to produce an output signal only when eachassociated pair of first and third selector means is in correspondingconditions, each of said second selector means being coupled to said ANDcircuit and responsive to said output signals to control the frequenciesof the control tones produced by said oscillators.
 27. A tonesubstitution system for use in a transmitter and comprising tone signalproducing means, first selector means coupled to said tone signalproducing means and being placeable in one of a plurality of conditionsto cause the tone signal to have a selected one of a correspondingplurality of first characteristics, a plurality of second selector meanscoupled to said tone signal producing means and each being placeable inone of a plurality of conditions to cause the tone signal to have aselected one of a corresponding plurality of second characteristics, anda plurality of third selector means coupled to said first selector meansand respectively coupled to said plurality of second selector means,each of said third selector means being placeable in one of a pluralityof conditions for rendering said first selector means or the associatedone of said second selector means operative to control thecharacteristics of the tone signal, when the condition of none of saidthird selector means corresponds to the condition of said first selectormeans the tone signal has the selected one of said firstcharacteristics, when the condition of one of said third selector meanscorresponds to the condition of said first selector means the tonesignal has the one of said second characteristics associated with theone of said second selector means coupled to said one third selectormeans.
 28. The tone substitution system set forth in claim 27, whereinthe number of second selector means equals the number of third selectormeans.
 29. The tone substitution system set forth in claim 27, whereinthe number of second selector means is the same as the number of thirdselector means and is no less than the number of said firstcharacteristics.
 30. The tone substitution system set forth in claim 27,wherein said tone signal producing means includes at least two variablefrequency oscillators for providing two control tones, the frequenciesof said control tones being determined by the conditions of saidselector means.
 31. The tone substitution system set forth in claim 27,and further comprising a plurality of electronic switching means havinginputs coupled to said first selector means, having inputs coupled tosaid plurality of second selector means and having outputs coupled tosaid tone signal producing means.
 32. A signal substitution system foruse in a transmitter including a tone generator for generating at leastone tone having a frequency selected from a plurality of possiblefrequencies, and comprising primary-tone selecting means coupled to thetone generator and placeable in a plurality of conditions to cause thetone produced by the tone generator to have a given frequency,substituting means coupled to said primary-tone selecting means andbeing placeable in a plurality of conditions corresponding to theconditions of at least some of the conditions of said primary-toneselecting means, said substituting means providing an output when thecondition thereof corresponds to the condition of said primary-toneselecting means, and substitute-tone selecting means coupled to the tonegenerator and placeable in a plurality of conditions to cause the toneproduced by the tone generator to have a different frequency, saidsubstitute-tone selecting means being coupled to said substituting meansand responsive to the output therefrom to cause the tone generator toproduce the tone having said different frequency instead of the tonehaving said given frequency.
 33. The signal substitution system setforth in claim 32, and further comprising electronic switching meanscoupled between said primary-tone selecting means and the tone generatorand being operative to cause the tone generator to produce a tone havingsaid given frequency in accordance with the condition of saidprimary-tone selecting means, said substitute-tone selecting means beingcoupled to said electronic switching means and being operative to causethe tone generator to produce a tone having said difference frequency inaccordance with the condition of said substitute-tone selecting means.34. The signal substitution system set forth in claim 32, wherein saidprimary-tone selecting means includes a multiposition manual switch. 35.A signal substitution system for use in a transmitter including a tonegenerator for generating a plurality of tones respectively havingfrequencies selected from a pluraLity of possible frequencies, andcomprising a plurality of primary-tone selecting means coupled to thetone generator and each placeable in a plurality of conditions to causethe tones produced by the tone generator respectively to have givenfrequencies, a plurality of substituting means respectively coupled tosaid plurality of primary-tone selecting means and each placeable in aplurality of conditions corresponding to the conditions of at least someof the conditions of the associated primary-tone selecting means, eachof said substituting means providing a signal when the condition thereofcorresponds to the condition of the associated one of said primary-toneselecting means, AND circuit means coupled to said plurality ofsubstituting means and responsive to the concurrence of a signal fromeach of said substituting means to provide an output, and a plurality ofsubstitute-tone selecting means coupled to the tone generator and eachplaceable in a plurality of conditions to cause the tones produced bythe tone generator respectively to have different frequencies, each ofsaid substitute-tone selecting means being coupled to said AND circuitmeans and responsive to the output therefrom to cause the tone generatorto produce the tones having said different frequencies instead of thetones having said given frequencies.
 36. A signal substitution systemfor use in a transmitter including a tone generator for generating atleast one tone having a frequency selected from a plurality of possiblefrequencies, and a primary-tone selector placeable in a plurality ofconditions to cause the tone produced by the tone generator to have agiven frequency, said signal substitution system comprising substitutingmeans for coupling to the primary-tone selector and being placeable in aplurality of conditions corresponding to the conditions of at least someof the conditions of the primary-tone selector, said substituting meansproviding an output when the condition thereof corresponds to thecondition of the primary-tone selector, and substitute-tone selectingmeans for operating the tone generator and placeable in a plurality ofconditions to cause the tone produced by the tone generator to have adifferent frequency, said substitute-tone selecting means being coupledto said substituting means and responsive to the output therefrom tocause the tone generator to produce the tone having said differentfrequency instead of the tone having said given frequency.
 37. Thesignal substitution system set forth in claim 36, and further comprisingelectronic switching means for coupling between the primary-toneselector and the tone generator and being operative to cause the tonegenerator to produce a tone having the given frequency in accordancewith the condition of the primary-tone selector, said substitute-toneselecting means being coupled to said electronic switching means andbeing operative to cause the tone generator to produce a tone havingsaid different frequency in accordance with the condition of saidsubstitute-tone selecting means.
 38. a signal substitution system foruse in a transmitter including a tone generator for generating aplurality of tones respectively having frequencies selected from aplurality of possible frequencies and a plurality of primary-toneselectors each placeable in a plurality of conditions to cause the tonesproduced by the tone generator respectively to have given frequencies,said signal substitution system comprising a plurality of substitutingmeans for respectively coupling to the primary-tone selectors and eachplaceable in a plurality of conditions corresponding to the conditionsof at least some of the conditions of the associated primary-toneselectors, each of said substituting means providing a signal when thecondition thereof corresponds to the condition of the associated one ofthe primary-tone selectors, AND circuit means coupled to said pluralityof substituting means and responsive to the concurrence of a signal fromeach of said substituting means to provide an output, and a plurality ofsubstitute-tone selecting means for coupling to the tone generator andeach placeable in a plurality of conditions to cause the tones producedby the tone generator respectively to have difference frequenceis, eachof said substitute-tone selecting means being coupled to said ANDcircuit means and responsive to the output therefrom to cause the tonegenerator to produce the tones having said different frequencies insteadof the tones having said given frequencies.